Double-wall corrugated pipes are widely used in municipal drainage, sewer systems, road culverts and underground cable protection due to their high ring stiffness, light weight and smooth inner bore.
Step 1: Raw Material Preparation
The main raw material for double-wall corrugated pipes is HDPE (High-Density Polyethylene), sometimes PVC-U for specific projects. The resin is mixed with required additives such as color masterbatch, UV stabilizer and processing aid according to the product formula. A good material mixing ratio directly affects the pipe's ring stiffness, surface finish and production stability.
Step 2: Extrusion and Melting
The mixed material is fed into a single-screw or twin-screw extruder. Inside the extruder barrel, the material is heated, compressed and melted into a uniform melt. For double-wall pipe production, two extruders are usually used - one for the outer corrugated layer and one for the inner smooth layer. The melt temperature is carefully controlled to ensure both layers bond perfectly.
Step 3: Corrugation Molding
This is the core step of DWC pipe production. The molten material enters a corrugator mold consisting of a series of moving mold blocks. The outer layer takes the corrugated shape under vacuum forming, while the inner layer remains smooth. The mold blocks move continuously with the pipe, forming the characteristic double-wall structure.
Step 4: Cooling and Sizing
After corrugation, the pipe passes through a vacuum cooling tank. Cooling water sprays onto the pipe surface to solidify the structure quickly. Proper cooling speed is critical - too fast may cause inner stress, too slow may deform the corrugations.
Step 5: Cutting and Stacking
The cooled pipe is cut to the required length (usually 6m or 12m per piece) by an automatic cutting saw. Finished pipes are then stacked, inspected and packed for delivery. Some production lines also add an online belling machine to form socket ends for easy installation.
| Process Stage | Key Equipment | Main Parameter | Common Issue to Watch |
|---|---|---|---|
| Material Mixing | Mixer / Hopper dryer | Drying temperature & time | Moisture causes surface bubbles |
| Extrusion | Single / twin-screw extruder | Melt temperature 180–220°C (HDPE) | Uneven melting → weak wall |
| Corrugation | Corrugator with mold blocks | Vacuum degree & line speed | Poor forming → shallow corrugation |
| Cooling | Vacuum cooling tank | Water temperature & cooling length | Uneven shrinkage → ovality |
| Cutting | Automatic cutting saw | Cutting length tolerance | Burrs or uneven cut face |
Common Raw Materials and Typical Applications
| Material | Typical Diameter | Main Application |
|---|---|---|
| HDPE | 110mm – 1200mm | Municipal drainage, sewer, road culvert |
| PVC-U | 110mm – 800mm | Building drainage, cable conduit |
| PP | 90mm – 600mm | Industrial drainage, chemical projects |
When selecting a double-wall corrugated pipe extrusion line, pay attention to three key points: extruder capacity, corrugator stability and cooling system efficiency. A stable production line reduces scrap rate and saves material cost in the long run.
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